I. Field of the Invention
The present invention relates to underwater alignment and connection of pipe in directional drilling and production applications. More particularly, the invention involves axially aligning and connecting tubular products used in trenchless beach crossings.
II. Related Art
Horizontal directional drilling is the application of drilling techniques to steer a drill along a prescribed pathway beneath an obstacle such as a river or beach. This pathway is then enlarged and improved such that a pipeline or conduit can be installed beneath the obstacle. The drill path takes a line below the surface to avoid disturbance of the banks or beach and thereby greatly reduces environmental impact. Typically, the drill path may be 30 or 40 feet beneath the surface.
Since the surface of the banks or beach are not disturbed, detrimental effects on water quality, vegetation, or wildlife are minimized. Additionally, by drilling beneath the surface of the beach, the risk of erosion is reduced or eliminated.
This invention has particular application to trenchless beach crossings. A trenchless beach crossing eliminates the need for digging a trench for laying the pipe. Typically, a drilling rig is set up behind the beach or sand dunes. From there, a hole is drilled at an angle to the surface. The hole continues horizontally below the surface of the beach (typically 30-40 feet below the surface) and exits at a remote submerged location after crossing beneath the beach.
Horizontal directional drilling is accomplished by use of a special drilling rig employing a non-rotating drill pipe with a fluid powered cutting tool at its downhole end. Direction is achieved by use of a small angular section in the body of the cutting tool, and by controlling the application of thrust on the drill string. This non-rotating pilot string drills a hole having a diameter of typically about 27/8 inches.
During the course of the drilling a larger drill pipe called the "wash pipe," typically having a diameter of about 5 inches, is rotated over the pilot string to reduce friction between the pilot string and sides of the bore. The wash pipe has a cutter on the end, and is guided by the pilot string.
Once the pilot bit exits the bore at a submerged location on the opposite side of the beach, the 5 inch diameter wash pipe is rotated to exit at that location. The pilot string is then withdrawn from the wash pipe.
Typically, the wash pipe will extend out the bore at the submerged exit point a distance of 20-50 feet along the sea bottom. The cutter is then removed from the end of the wash pipe.
Another 5 inch diameter drill pipe referred to as the "work string" is then made up on shore, then towed offshore. The work string typically includes a swivel and a reamer for improving the well bore. This work string is connected to the wash pipe, then pulled back through the well bore.
The prior art method for connecting the wash pipe and work string involved using a barge to raise the end of the wash pipe to the surface, and connecting the work string to the wash pipe on board the barge. Typically, the ends are threaded together by rotating one end while restraining the other, with one pipe having a pin end connection and the other pipe having a box end connection. A swivel and reamer typically are connected between the wash pipe and the work string.
Then the connection is lowered to the sea bottom, and the wash pipe and reamer are rotated as the work string is pulled back through the bore. The wash pipe is removed from the hole joint by joint until the reamer reaches the foot of the drilling rig.
A pipeline is then either prepared offshore or onshore and towed offshore to be connected to the work string. The end of the work string and the pipeline are then raised to the surface to connect them together. As before, one pipe has a box end connection and one has a pin end connection. A swivel and "bullet nose" reamer typically are connected between the work string and the pipeline to further improve and assist the pipeline into the bore.
After the pipeline is connected to the work string, it is lowered to the sea bottom and the work string, bullet nose and pipeline are pulled back through the well bore. The work string is removed from the hole joint by joint until the bullet nose reaches the foot of the drill rig. The pipeline is then safely in place below the beach.
One problem that has been encountered with the prior art method is the time and expense for use of a barge at an offshore location. Also, underwater connection has not been practical because the pipes are often misaligned on the sea bottom and have no means of restraint to facilitate threading them together.